The present invention relates to a distribution system for a frequency standard, and more particularly pertains to a method and apparatus for distributing a reference signal that has a standard frequency and phase over RF links; said system adaptively correcting for any phase perturbation introduced into the link.
There are many applications in existence which require the phase synchronization of two signals respectfully generated at a first and second station where the stations are remotely located from each other. Thus, for example, a reference signal from a hydrogen maser frequency standard may need to be produced in phase synchronization at a multiplicity of sites. In order to avoid the high cost of separate hydrogen maser frequency standards, at each site and eliminate the skew which is inherent in systems using separate frequency standards, a system for phase synchronizing a reference signal with a second slave signal is needed.
Prior art systems of this type are known. These systems employ a closed loop signal path in which a reference signal is transmitted from a first to a second remote station. The remote station then retransmits the received signal back to the first station. The received retransmitted signal from the remote station is mixed with a reference signal at that first station to form phase information which is used on the signal transmitted from the first station to compensate for the phase distortion caused by transmission path delays.
A major problem exhibited by these systems is the interference between the receiver and transmitter at each of the stations. Each station, master station or slave station, has both a receiver and transmitter. The present invention alleviates this interference problem by both reducing the noise coupling between the transmitter and receiver at any one station and by providing each station with the ability to distinguish between a transmitted and a received signal. In addition, the present invention is not affected by movement causing a change in the distance between the master and slave station, as is the case for prior art systems.